Russian physicists together with their European colleagues have mastered recording information on quasiparticles excitons, the mediators between a photon and an electron during energy transfer

MOSCOW, March 10. /TASS/ Russian physicists from ITMO University together with their European colleagues have mastered recording information on quasiparticles excitons, the mediators between a photon and an electron during energy transfer, the ITMO press office said. Based on the variation of a laser beam’s parameters, the new approach will assist in creating compact optoelectronic devices for storage and rapid processing of optical signals.

In the new study, the researchers from the ITMO University, Germany’s Leipzig University, and Eindhoven Technical University (Netherlands) by changing the light parameters of a laser beam managed to not only generate excitons at room temperature but also to record information using them. This was possible because of applying a special class of material called metalorganic frameworks.

What are excitons?

Excitons are quasiparticles corresponding to a coupled pair of an electron and a hole. They can appear in material while undergoing irradiation with photons and therefore they act as mediators between the photon and electron during energy transfer. According to the scientists, such intermediation could be helpful in the future in creating principally new class of energy-effective and compact devices. However, up to now, the tested technical samples can operate only at low temperatures or they are extremely hard to produce which hinders their mass adoption.

New material for recording optical information

In their study, the scientists used the metalorganic frameworks (MOF), a multilayer structure consisting both of organic and inorganic components, synthesized at ITMO. Different layers of this structure are attracted to one another due to intermolecular forces with the interlayer space filled with an organic liquid to avoid spontaneous contacts.

Using a laser, the researchers were able to excite two types of excitons in the MOF: inter-and intra-layer. The first type is created when the photon absorbed by the material becomes an electron-hole pair inside one layer while the second type appears when the created electron and hole belong to different layers. After some time, both types of quasiparticles decompose with the re-emission of energy in the form of photons.

The lifespan of the interlayer excitons is relatively short, but their high density and mobility ensure the possibility of using these quasiparticles for light generation, for example, in LEDs and lasers. In contrast, intra-layer excitons are more persistent but quite inactive which led the scientist to the idea to use them for recording the information on MOF.

"Using a laser, we heated the crystal locally," Valentin Milichko, the article’s first author and senior lecturer at ITMO University’s Nanophotonics and Metamaterial Faculty, commented. "At the irradiated spot, the layers were stuck together and the emission of excitons disappeared while the rest of the crystal was continuously emitting the luminescence. This implies that we recorded one bit of information with the record in the form of a dark spot stored for many days."

"To erase the data, one should simply dip the MOF to the same organic liquid which holds the layers together. The crystal itself will not be damaged, but the recorded information disappears," Milichko added.